1. Field of the Invention
The present invention relates to an electric rotating machine usable as a wheel-in motor for automobiles.
2. Description of Related Art
Recent years have seen a remarkable progress in electric motorization in automobile drive systems. In particular, much attention has focused on the “electric wheel”. In this specification, the term “electric wheel” refers to a wheel of an automobile in which whole or parts of a stator and a rotor of an electric rotating machine for driving the wheel are built in this wheel.
Japanese Patent Application Laid-open No. 8-289501 proposes an inner-rotor type electric wheel in which a stator (armature) having a three-phase winding is disposed in a radially outer space of the wheel, and a magnet field type rotor is disposed in a radially inner space of the wheel. Japanese Patent Application Laid-open No. 2004-306733 proposes an outer-rotor type electric wheel in which a stator (armature) having a three-phase winding is disposed in a radially inner space of the wheel, and a magnet field type rotor is disposed in a radially outer space of the wheel.
However, the proposed electric wheels have a problem in that it becomes difficult to manufacture the wheel suspension system (wheel damper, for example) because of the increase of the unsprung mass resulting from the provision of the electric rotating machine. The provision of the electric rotating machine also pose a problem that the gear shift performance is degraded, because the rotational inertial mass of the wheel increases by that of the electric rotating machine.
To remove these problems, it is necessary that the electric rotating machine is reduced in weight. However, since reducing the weight of the electric rotating machine inevitably reduces its output power, it is difficult for the electric wheel to have both a sufficiently small inertial mass and a sufficiently large driving force. For such reason, no electric wheels are put to practical use in automobiles so far.